In metal plating processing, the bath constituents change as the plating process proceeds, either because certain constituents are depleted, or because of product drag-out, that is, a certain amount of plating solution is carried out of the bath as the plated products are removed. The drag-out varies depending on the shape and size of the plated products. Moreover, the bath can become contaminated over time, and/or the pH of the bath can change.
The conventional response to this problem is to have an operator manually replenish bath constituents based on a predetermined replenishment schedule. However, such a schedule does not account for changes peculiar to a particular bath. As a result, it is difficult to ensure a consistent plating thickness and consistent quality from one plating run to another. Moreover, as a practical matter, the bath constituents cannot be replaced as often as is necessary to ensure constant bath composition.
Accordingly, it is necessary for a manufacturer of plated goods to use a target plating thickness greater than the customer's specification in order to provide a margin which will allow for variations in the plating thickness. This is extremely inefficient and can result in unnecessary added expense. This expense can become very significant when plating with precious metals.
Moreover, many customers are requiring that their suppliers have quality control processes in place. With conventional processing, it is impossible to ensure the six-.sigma. (a standard deviation of 0.000001) plating accuracy required by many customers. Plating companies may lose customers if they cannot meet six-.sigma. quality control requirements.